Although positive sensory feedback in sensorimotor control has been evidenced in many neural systems, the role of this retroaction is still unclear. The general aim of this exploratory/developmental R21 application is to understand the function of positive sensory feedback in closed-loop neural networks. We have developed an experimental model of positive sensory feedback in the rat vibrissa system. This model consists of a novel slice preparation of the brainstem that contains the nuclei of the vibrissa-trigemino-facial (VTF) loop. We have shown that in this preparation, stimulation of sensory inputs elicits a delayed, polysynaptic and excitatory response in vibrissa motoneurons, which are the output cells of the VTF circuit. The specific goal of this application is to characterize the role of positive sensory feedback in vibrissa motoneurons using the framework of weakly coupled self-sustaining oscillators. We plan to: 1) describe the open-loop dynamics of the VTF circuit by combining intracellular electrophysiology, phase sensitivity and entrapment analysis.2) quantify the behavior of the VTF circuit in the closed-loop configuration in which a neuromorphic circuit that plays the role of vibrissae.3) develop, in collaboration with Prof. David Golomb, a plausible computational model of the VTF loop using the preceding experimental results to study the stability of this loop and to explore its role in computo. The presence of positive sensory feedback in facial motoneurons could be of particular importance to trigemino-facial disorders in humans. Our research could provide clues to understand the still unknown etiology of diseases such as blepharospasm.